Method of making a superconductor by sintering powdered metals



United States Patent 3,325,888 METHQD 0F MAKENG A SUPERCONDUCTOR lBY SHNTERHNG PUWBJERED METALS heldon Weinig, Hastings on Hudson, N.Y., George T. Murray, Woodclitt Latte, and Steven D. Hurwitt, Park Ridge, N11,, and Drory H. Ben-Israel, Spring Valley, N.Y., assignors to Materials Research Corporation, filrangcburg, N.Y., a corporation of New York No Drawing. Filed Feb. 8, 1963, Ser. No. 257,108 Ciairns. (Cl. 29-420) This invention relates to electrical conductors having superconducting properties at extremely low temperatures and more particularly to such conductors which can be bent without afiecting their superconducting properties.

Recently considerable interest has been shown in the use of superconducting wire and the like for transmission of electrical power on an industrial or commercial scale. It has been determined that the cost of maintaining the conductor in a cryogenic environment is justified by the substantial elimination of power losses in the system. The use of superconductors is contemplated for various propulsion systems, cryogenic airborne computers, controlled fusion systems, magnetic-hydrodynamics, in the magnetic systems of nuclear accelerators, as well as in other varied applications.

Superconductivity is defined as the state in which materials exhibit almost zero resistance to flow of electric current. This phenomenon occurs at extremely low temperatures. Niobium-tin has the highest transition temperature, i.e. the point at Which the material starts super conducting, of any material so far investigated. Nb Sn becomes superconducting at 18 Kelvin (-255 C.), however, after bending the superconductivity is usually lost. Since the most immediate application of this material is as a winding for magnets, this has been a problem which has plagued the art.

The method of the present invention has provided a Nb sn superconductor which can be bent without loss of the superconducting properties and consequently constitutes a breakthrough which provides the art with a long sought product.

Briefly the method of the present invention involves pelletizing a mixture of elemental niobium and tin powders containing about 70-80% by weight niobium and about 30-20% by Weight tin, sintering the pellets at about 950- ll00 C. for about 4-48 hours to form a Nb-Sn alloy; inserting said pellets in a ductile metal sheath such as copper; drawing, rolling or swaging said sheath to produce a wire or ribbon or the like having a Nb-Sn core and an outer layer of the ductile metal, and then subjecting the resultant material to an elevated temperature of about 950-1100 C. for about 6-48 hours. Other objects and features of the present invention will appear in the following specification and claims.

Describing the present invention more specifically, elemental niobium and tin powders of about 325 mesh are thoroughly mixed in roughly a 3/1 ratio of niobium to tin, eg from about 70% to about 80% niobium and from about 30% to about 20% tin. This powder mixture is then pressed to form pellets or slugs. The compaction pressure is of the order of about 120,000 psi. which provides pellets or slugs having a density of about 7 grams/ cm The pellets are then sintered at a temperature of 950-1100 C. for 4-48 hours, preferably at about 1000 C. for about 16 hours, to form a Nb-Sn alloy, e.g. Nb Sn. Next a sheath or tube or the like of a ductile metal such as copper, nickel, Monel, inconel, niobium or stainless steel is packed tightly with the Nb-Sn alloy pellets. It also may be desirable to reduce the pellets to powder form and then fiil the ductile metal tube with powder.

The filled tube or sheath is then reduced to the desired size of wire or ribbon by rolling, drawing, swaging, or any combination thereof and then the wire or ribbon is annealed or subjected to an elevated temperature, in the range of 950-1100 C. for about 6-48 hours, preferably at about 950 C. for 16 hours.

For example, starting with an initial mixture of 325 mesh powder containing by weight niobium and 25% by weight tin pellets were formed and sintered at 1000 C. for 16 hours. Then the pellets were placed in a 0.5 inch ID. copper tube and were drawn down to a wire having an OD. of 0.03 inch. The wire carried 60 amperes at a temperature of 4.2 K. in 100,000 gauss field after bending around a inch diameter mandrel.

In another case, a similarly formed 0.020 diameter Wire carried amperes current in a zero field at 42 K.

The initial diameter of the tube may be any convenient size and the final diameter of the drawn conductor may vary from about 0.005 inch to about 0.050 inch, depending on the intended end use thereof.

A modified method according to the present invention involves the similar mixin and preparation of the initial pellets and sintering to provide the niobium-tin alloy. Then the pellets are again reduced to about 325 mesh powder and such powder is mixed with up to about 30% by Weight of a mixture of powdered elemental niobium and tin being in substantially the same relative proportions as in the powdered alloy. Then the resulting mixture is pelletized, the pellets inserted into a niobium tube or sheath and the latter is reduced to a wire or ribbon and then subjected to a temperature of about 950-1l00 C. for about 6-8 hours.

The superconducting wire or ribbon produced by the above methods provide reliability of long lengths due to ease of fabrication, can be bent without afiecting the superconductivity, and are in fact less expensive to produce than prior art materials having the same properties. Such superconductors have high current carrying capacities in high strength magnetic fields and are suitable for use in solenoids, magnets, gyroscopes, switches, etc.

In addition to the use of niobium and tin alloys, the present methods can also be used with superconducting alloys of V Si and V Ga, and superconductors fabricated which exhibit substantially the same properties as indicated above for the Nb-Sn superconductors.

While certain embodiments of the invention have been shown and described, it is to be understood that changes and additions may be made by those skil'ed in the art without departing from the scope and spirit of the invention.

What is claimed is:

1. The method of fabricating a superconductor comprising the steps of mixing niobium and tin powders in the proportion by weight, of about 70-80% niobium and about 30-20% tin, pelletizing such mixture, sintering said pellets at about 950-ll00 C. for about 4-48 hours, reducing said pellets to a powder and mixing the latter said powder with up to about 30% by weight of a mixture of powdered niobium and tin being in substantially the same relative proportions as in said pellets, pelletizing such admixture, inserting the latter pellets into a ductile metal sheath, reducing the cross-section of said sheath to a predetermined size to form a conductor, subjecting said conductor to a temperature of about 950-1100 C. for about 6-48 hours.

2. The method of fabricating a superconductor comprising the steps of mixing niobium and tin powders in the proportion by weight of about 70-80% niobium and about 30-20% tin, pelletizing such mixture, sintering said pellets at about 950-1100 C. for about 4-48 hours, reducing said pellets to a powder and mixing the latter said powder with up to about 30% by weight of a mixture of powdered niobium and tin being in substantially the same relative proportions as in said pellets, pelletizing such admixture, inserting the latter pellets into a sheath of a metal selected from the class consisting of copper, nickel, Monel, Inconel, niobium and stainless steel, reducing the cross-section of said sheath to a predetermined size to form a conductor, subjecting said conductor to a temperature of about 9501100 C. for about 6-48 hours.

3. The method of fabricating a superconductor comprising the steps of mixing niobium and tin powders in the proportion by weight of about 70'80% niobium and about 30-20% tin, pelletizing such mixture, sintering said pellets at about 9501l0-0 C. for about 4-48 hours, reducing said pellets to a powder and mixing the latter said powder with up to about 30% by weight of a mixture of powdered niobium and tin being in substantially the same relative proportions as in said pellets, pelletizing such admixture, inserting the latter pellets into a ductile metal tube, reducing the cross-section of said tube to a predetermined size to form a conductor, subjecting said conductor to a temperature of about 950-1100 C. for about 6-48 hours.

4. The method of fabricating a superconductor comprising the steps of mixing niobium and tin powders in the proportion by weight of about 7080% niobium and about 30-20% tin, pelletizing such mixture, sintering said pellets at about 950-1100 C. for about 4-48 hours, reducing said pellets to a powder and mixing the latter said powder with up to about 30% by Weight of a mixture of powdered niobium and tin being in substantially the same relative proportions as in said pellets, pelletizing such admixture, inserting the latter pellets into a niobium tube, reducing the cross-section of said tube to a predetermined size to form a conductor, subjecting said conductor to a temperature of about 950 C. for about 16 hours.

5. The method of fabricating a superconductor comprising the steps of mixing niobium and tin powders of about 325 mesh in the proportion by weight of about -80% niobium and about 30-20% tin, pelletizing such mixture at a compaction pressure of about 120,000 p.s.i. to provide a pellet density of about 7 grams/em sintering said pellets at about 9501100 C. for about 448 hours, reducing said pellets to a powder of about 325 mesh, and mixing the latter said powder with up to about 30% by weight of a mixture of powdered niobium and tin being in substantially the same relative proportions as in said pellets, pelletizing such admixture at a compaction pressure of about 120,000 psi. to provide a pellet density of about 7 grams/cm. inserting the latter pellets into a niobium tube, reducing the cross-section of said tube to a predetermined size to form a conductor, subjecting said conductor to a temperature of about 950 C. for about 16 hours.

References Cited UNITED STATES PATENTS 3,084,041 4/1963 Zegler. 3,162,943 12/1964 Wong 148-115 3,218,693 11/1965 Allen.

HYLAND BIZOT, Primary Examiner. 

1. THE METHOD OF FABRICATING A SUPERCONDUCTOR COMPRISING THE STEPS OF MIXING NIOBIUM AND TIN POWDERS IN THE PROPORTION BY WEIGHT OF ABOUT 70-80% NIOBIUM AND ABOUT 30-20% TIN, PELLETIZING SUCH MIXTURE, SINTERING SAID PELLETS AT ABOUT 950-1100*C. FOR ABOUT 4-48 HOURS, REDUCING SAID PELLETS TO A POWDER AND MIXING THE LATTER SAID POWDER WITH UP TO ABOUT 30% BY WEIGHT OF A MIXTURE OF POWDERED NIOBIUM AND TIN BEING IN SUBSTANTIALLY THE SAME RELATIVE PROPORTIONS AS IN SAID PELLETS, PELLETIZING SUCH ADMIXTURE, INSERTING THE LATTER PELLETS, PELLETIZING METAL SHEATH, REDUCING THE CROSS-SECTION OF SAID SHEATH TO A PREDETERMINED SIZE TO FORM A CONDUCTOR, SUBJECTING SAID CONDUCTOR TO A TEMPERATURE OF ABOUT 950-1100*C. FOR ABOUT 6-48 HOURS. 